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Tropical Storm Irwin Forecast Discussion Number 27
2017-07-29 04:32:52| National Hurricane Center (East Pacific)
Issued at 800 PM PDT Fri Jul 28 2017 000 WTPZ45 KNHC 290232 TCDEP5 Tropical Storm Irwin Discussion Number 27 NWS National Hurricane Center Miami FL EP102017 800 PM PDT Fri Jul 28 2017 Microwave data indicate that inner-core convection has recently developed near Irwin's center; however, the convection is not all that deep, with cloud top temperatures no colder than about -65C. Even though Dvorak intensity estimates from TAFB and SAB are T3.5/55 kt, the UW-CIMSS ADT and SATCON estimates are significantly lower, so the initial intensity will remain 50 kt. Vertical shear does not appear that it will be too prohibitive for the next 24 hours, and in fact, some models like the HWRF and HCCA suggest that Irwin could gain a little strength during that time. However, Irwin should reach waters colder than 26C in about 36 hours, which will induce a marked weakening trend. The NHC intensity forecast closely follows a blend of HCCA and the ICON intensity consensus, and it now shows Irwin becoming a tropical depression by day 3. The global models no longer show Irwin being absorbed by Hilary, probably because Hilary will reach colder waters sooner and will not be energetic enough to be the dominant system. The guidance shows one of two options: Irwin absorbing Hilary or the two staying as separate system. Either way, these scenarios required keeping Irwin through day 4, but as a remnant low since ocean waters will be quite cold. Center fixes off of recent microwave images indicate that Irwin had been drifting southward or meandering for much of the day. As Hilary moves northwestward, Irwin is expected to get pulled slowly northward during the next 24-36 hours, and then accelerate north-northwestward on the east side of Hilary on days 2-4. There is a fair amount of spread among the track models, especially after 48 hours, but the NHC track forecast is close to the tight clustering consisting of the GFS, ECMWF, HCCA, TVCN. FORECAST POSITIONS AND MAX WINDS INIT 29/0300Z 14.8N 124.7W 50 KT 60 MPH 12H 29/1200Z 15.0N 124.7W 55 KT 65 MPH 24H 30/0000Z 16.0N 124.8W 55 KT 65 MPH 36H 30/1200Z 17.7N 125.1W 50 KT 60 MPH 48H 31/0000Z 20.0N 125.9W 45 KT 50 MPH 72H 01/0000Z 24.9N 128.8W 30 KT 35 MPH 96H 02/0000Z 27.5N 131.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 03/0000Z...DISSIPATED $$ Forecaster Berg
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